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The preferred embodiments of the present invention generally relate to a mobile C-arm based x-ray system for constructing three dimensional (3-D) volumetric data sets and using the data sets in diagnostic and interventional medical procedures. More specifically, at least one preferred embodiment of the present invention relates to a mobile C-arm based x-ray medical imaging system that constructs three-dimensional volumetric data sets of digital x-ray images, based, in part, on coordinate information for patients and the x-ray receptor, and uses the data sets for diagnostic and interventional procedures to be carried out.
Conventional medical imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), use sophisticated mechanical gantry structures to support patients and equipment used to construct patient imaging data sets. The CT and MRI data sets are formed from a plurality of scans in which the exact position of the patient is known from the relation between the mechanical gantry and the patient table formed integral with the gantry. For instance, CT systems use a circular gantry that supports a continuously rotating fan beam x-ray source and an opposed arcuate detector array. The fan beam x-ray source and detector array continuously rotate within the gantry. The CT system also includes a patient table integral with the gantry. The table moves the patient through the gantry at predefined incremental steps while the fan beam x-ray source continuously rotates. The mechanical interconnection of the gantry and table in the CT system maintain a known relationship between the position of the patient and of the x-ray source and detector array at all times, and thus is able to construct a set of 2-D images aligned in a known relationship to one another in order to construct a 3-D volumetric data set of the images. Once the 3-D volume is constructed, individual slices of the patient may be obtained to present to the doctor desired views, such as the sagittal, coronal and axial views; or segmented or rendered image views. MRI systems maintain a similar mechanical interconnection between the gantry holding the magnet coils and patient table.
However, CT and MR systems are extremely complex, large and expensive. In the more recent history, intraoperative MR and mobile CT systems have been proposed. However, these intraoperative MR and mobile CT systems still require a configuration comprising a patient table formed integrally with the gantry. Many intraoperative and diagnostic procedures do not justify or warrant the cost of MR and CT systems, mobile or otherwise. Further, intraoperative MR and mobile CT systems are still quite large and take up a significant portion of an operating room.
Today, many diagnostic and surgical procedures are carried out using a mobile C-arm type x-ray system in a fluoroscopy or digital spot mode. Mobile C-arm x-ray systems are more commonly found in an OR or interoperative hospital and clinical facilities as such systems are much smaller, less complex and less expensive than CT and MR systems. Conventional mobile C-arm systems have been used during surgical procedures by performing standard fluoroscopic x-ray imaging to acquire one or more x-ray images of the patient during the procedure. The most common x-ray images obtained using the mobile C-arm include the AP and lateral views. By way of an example, during a surgical planning phase, the doctor may obtain two exposures/shots, namely one AP view and one lateral view to initially observe and study the region of interest. In a spinal procedure, the doctor next will resect tissue from the region of interest (ROI) to expose a bony portion of interest. Next, the doctor places the surgical instrument or tool near the bony portion of interest, with the instrument or tool located at a desired position and orientation at which the doctor desires to carry out the surgical procedure. The doctor next typically obtains two new exposures/shots (AP and lateral) of the ROI and instrument to view the position and orientation of the instrument/tool relative to the bony portion of interest. Then the doctor begins the surgical procedure, such as drilling a hole in the bone or the like. At various stages along the surgical procedure, the doctor obtains new pairs of exposures/shots (AP and lateral) to determine the progress of the procedure. This process is repeated until the tool reaches a desired destination. The foregoing process requires several exposures to be taken of the patient, thereby causing the patient to receive a large x-ray dose, even though it is preferable to minimize the radiation dosage required to complete a procedure.
C-arm based systems have a configuration of joints and interconnects that permit the doctor to move and rotate the C-arm through several directions of movement, such as an orbital tracking direction, longitudinal tracking direction, lateral tracking direction, transverse tracking direction, pivotal tracking direction, and xe2x80x9cwig-wagxe2x80x9d tracking direction. The C-arm may be moved through each of the foregoing tracking directions by releasing mechanical locks at the appropriate joints and interconnects.
At least one C-arm type system has been proposed that includes a mechanical motor to drive the C-arm (and thus the x-ray source and image intensifier) in the orbital tracking direction, namely in an arcuate path within the plane defined by the C-arm frame. As the motor moves the C-arm in the orbital tracking direction, a series of exposures are taken. The series of exposures are combined into a data set for display as a three-dimensional volume. However, the motor driven C-arm system is only useful for diagnostic procedures, not interventional operations, since the image frames are not correlated to the patient location and alignment.
A need remains for an improved C-arm based system capable of constructing 3-D volumetric data sets of patient and instrument information and capable of displaying slices, segments or rendered volumes of data at any desired viewing angle for use during diagnostic and interventional procedures.
According to one aspect of a preferred embodiment, a medical imaging system is provided having a C-arm with an x-ray source for generating x-rays and a receptor device for receiving x-rays and deriving a fluoroscopic image from the x-rays received. The C-arm moves the x-ray source and receptor device along an image acquisition path between at least first and second image acquisition positions. An acquisition module obtains a series of 2-D fluoroscopic images, wherein first and second fluoroscopic images are obtained when the x-ray source and receptor are located at the first and second image acquisition positions, respectively. An image processor constructs a 3-D volume of object voxels based on the series of fluoroscopic images. A monitor displays images based on the 3-D volume, such as 3D renderings, patient slices and the like. A position tracker monitors the position of the C-arm and patient at each of the positions through the series of exposures and provides position information for the patient and the receptor for fluoroscopic images. The C-arm may be manually, mechanically or automatically moved along the image acquisition path.
According to at least one alternative embodiment, an image processor constructs a computed tomography volume from a series of 2-D fluoroscopic images. The image processor transforms multiple 2-D fluoroscopic images into 3-D volumetric data sets. The image processor may perform an iterative reconstruction technique to construct the 3-D volume. Alternatively, the image processor may perform a back projection technique to construct the 3-D volume.
According to at least one alternative embodiment, the C-arm is rotatably mounted to a base that moves the C-arm along an orbital rotation path to cause the x-ray source and receptor device to follow an arc about an orbital axis aligned perpendicular to a plane defined by the C-arm. According to at least one alternative embodiment, a mobile base is provided having wheels. The C-arm may be mounted to the base and the base may be movable on the wheels along a lateral rotation arc formed tangentially to an orbital axis traversing the C-arm plane to move the x-ray source and receptor device along a lateral image acquisition path between the first and second positions. A pivot member may be provided. The pivot member may pivot the C-arm about a pivot axis contained in and extending along the plane containing the C-arm. The pivot member pivots the x-ray source and receptor device about a pivotal image acquisition path between the first and second positions.
According to a further alternative embodiment, the acquisition module acquires a sequence of 2-D fluoroscopic images at predetermined positions spaced along the imaging path. Optionally, the acquisition module may obtain 2-D fluoroscopic images at an even interval along the image acquisition path. The even interval may be at approximately every five degrees of rotation of the C-arm. The acquisition module continuously calculates the position of the C-arm with respect to a coordinate reference system and triggers the x-ray source to generate exposures when the C-arm reaches predetermined positions along the imaging path.
In one embodiment, the first and second positions may constitute the beginning and ending positions, respectively, along an arcuate range of motion of the C-arm. The beginning and ending positions may be between 145 degrees and 190 degrees apart.
The preferred embodiments of the present invention may be used in a variety of diagnostic procedures, interventional surgical applications and the like, such as in orthopedic procedures, spinal studies and applications, joint replacement procedures and the like. A spinal application may involve attaching a pen or screw to a vertebra, such as the cervical, thoracic or lumbar. The vertebra represents a complex anatomy that may not be satisfactorily illustrated through AP and lateral fluoroscopy views. The AP and lateral views may not necessarily show adequate intricate detail of the vertebra. Preferably, spinal applications involve the display of sagittal, coronal and axial views to present the cross-section of the spinal column in a slice by slice format. According to at least one preferred embodiment, sagittal, coronal and axial views may be obtained from the 3-D volume data set obtained by the C-arm.
As the doctor performs the spinal surgery, the instrument or tool may be superimposed upon one or more of the 2-D or 3-D images presented to the doctor. The position of the instrument or tool is continuously and repeatedly updated in real-time in order to follow the movement of the instrument or tool relative to the patient""s spinal column.
An example of a general orthopedic procedure, in which at least one preferred embodiment of the present invention may be used, involves fracture reduction, such as when setting a broken bone. During a fracture reduction operation, one or more tracking devices may be attached to one or more points on the fractured bone. The 2-D or 3-D images obtained illustrating the fractured bone may be used for surgical planning and/or alignment. The 2-D or 3-D images may further be used during implementation of the fracture reduction procedure (i.e. set the bone) to obtain views in any desired orientation of the fractured bones. As the fracture is closed, the 2-D or 3-D images may be viewed in any desired orientation to determine if the bones are being properly aligned.
Another example of a general orthopedic procedure, in which at least one preferred embodiment of the present invention may be used, involves joint replacement, such as when replacing a knee with a prosthesis. A knee prosthesis includes a ball and receiving joint. A notch is cut in the bone on one side of the knee and the ball is inserted therein. A notch is cut in the bone on the other side of the knee and the receiving joint is inserted therein. It is important that the ball and receiving joint be properly aligned within the bone notches since if either is misaligned by a few degrees, the foot will not be aligned properly. Also, misalignment within the ball and joint causes the prosthesis to prematurely wear out since the joints are designed to have an equal load. If the load is unbalanced by only a few degrees, the joint will wear prematurely.
General orthopedic and spinal procedures are not considered to warrant the need for a computed tomography system, nor justify the cost added to the operation for a CT system. However, typically, fluoroscopy systems are present in, or available to, most operating rooms and thus more readily available for used during general orthopedic and spinal procedures. Volumetric reconstruction with the fluoroscope affords the doctor the ability to conduct surgical planning quickly while a patient is anesthetized on the table. Within a few minutes of the surgical planning phase (e.g. preoperative planning), the doctor is able to execute the plan to afford proper alignment (e.g. interoperative navigation) and to verify quality assurance. Hence, at least one preferred embodiment of the present invention enables a doctor to verify that a plan has been properly executed. In accordance with at least one preferred embodiment of the present invention, imaging data may be collected during an intraoperative procedure (e.g. interoperative data collection), without any need for pre-imaging. By affording interoperative data collection, a patient need not be moved to a separate room for image collection, but instead, the images may be obtained by the C-arm while the patient is anesthetized and prepped for surgery.